Polyisocyanate compositions per se have been utilized for years in association with polyols in the presence of catalysts and blowing agents to manufacture polyurethane foams. For example, certain polymethylene polyphenylene polyisocyanate (PMDI) compositions have been employed in view of its capacity for the absorption of excess isocyanate in the foam. However, PMDI, as currently formulated in the art, i.e., containing at least about 65.0 weight percent oligomers of MDI, is generally considered unsuitable for this purpose because of its relatively high viscosity of at least about 200 centipoise at 25.degree. C. In an effort to address this disadvantage, attempts have been made to dilute known PMDI compositions with a solvent such as 1,1,1-trichloroethane to reduce the viscosity. However, the resulting solution is considered to be environmentally unsuitable.
Further, the use of such a solvent adds to processing costs which in turn is reflected in the cost of the resulting product.
Thus, in an effort to address the need in the art for a PMDI composition, lower viscosity PMDI compositions such as those having a viscosity of about 50 centipoise at 25.degree. C. have been employed. However these compositions also resulted in certain disadvantages such as a sensitivity to temperatures below about 60.degree. F. apparently due to the high concentration of 4,4' MDI, i.e., 65.0 weight percent or more. As a consequence of this temperature sensitivity, in order to be useful, the resulting polyisocyanate compositions require heated storage and transportation, thus increasing costs.